Title

High Potassium Activation And Beta-Adrenergic Relaxation Of The Guinea Pig Taenia Coli (smooth Muscle, Calcium)

Date of Award

1983

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Abstract

The activation of the guinea pig taenia coli by 145 mM K('+)/0 Na('+) was characterized with respect to contractility, Ca('2+) influx and the net Ca('2+) gain. The Ca('2+) influx rate was determined with a one minute pulse method and a prelabel (in PSS) technique. Both methods demonstrated a high K('+)-stimulated Ca('2+) influx during the first minute of high K('+) exposure. The prelabel technique detected about four times more Ca('2+) than did the pulsed method. Labelling of the Ca('2+) pool that contributes to the K('+)-stimulated influx was found to have a rate similar (t(, 1/2) about 40 seconds) to that for loss of Ca('2+) from the pool responsible for the phasic contraction. This rate is also similar to that for extracellular free Ca('2+) diffusion. Using the prelabel influx data, the Ca('2+) influx was found to quantitatively account for the net Ca('2+) gain induced by high K('+). D600, a Ca('2+) cannel blocker, was able to inhibit two Ca('2+) pathways that were found to be activated by high K('+) depolarization. There is a "fast" Ca('2+) channel associated with the K('+)-stimulated influx and the phasic contraction, and a "slow" channel responsible for Ca('2+) influx during the tonic contraction. Pretreatment of the quinea pig with agents that increase cAMP (isoproterenol, RO 20-1724 or dibutyryl cAMP) was able to inhibit Ca('2+) influx through the "fast", but not the "slow", Ca('2+) channels. Addition of isoproterenol or RO 20-1724 to tissues tonically contracted with high K('+) resulted in relaxation. There was no change in the Ca('2+) influx rate or net gain during relaxation. Also, RO 20-1724 was not found to have any effect on unidirectional Ca('2+) efflux. It was concluded that inhibition of Ca('2+) influx or stimulation of Ca('2+) extrusion was not responsible for the observed relaxation. The results suggest that (beta)-adrenergic relaxation is due to an intracelluar process such as Ca('2+) sequestration.

Keywords

Health Sciences, Pharmacology

Link to Full Text

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